Using the MCNP code, we explore three different 99Tc loading patterns in pressurized water reactor (PWR) burnable poison rods (BPRs). We also calculate the effects on the PWR keff and boric acid concentration readjusted amount after loading 99Tc transmutation material into PWR BPRs. Finally, we carry out the transmutation rate and depletion calculation.

After the 99Tc transmutation material is mixed homogeneously with burnable poison (BP) in the BPRs, keff slightly increases. As the amount of 99Tc coating on the BPRs increases, keff decreases gradually and slightly; this result is similar to the tendency of keff to decrease after applying a thin-layer coating of minor actinide in the BPRs. Our calculation results show that as the coating thickness of 99Tc in the water gap of BPRs increases, keff decreases correspondingly. The more BPR water gaps are filled in with 99Tc transmutation material, the sharper is the decrease of keff. If 99Tc fills in the water gaps of 12 BPRs of each fuel assembly, the coating thickness is 0.02 cm, and the corresponding total 99Tc coating amount is 206.76 kg. This is the annual 99Tc yield of more than three PWRs.

Our calculations also indicate that the more 99Tc is loaded into the PWR, the more boric acid concentration needs to be reduced in the coolant. For instance, if the 99Tc coating thickness in the water gaps is 0.02 cm, when 99Tc fills in 12 BPR water gaps of each fuel assembly, a boric acid concentration of 75 parts per million must be reduced from the PWR primary coolant to allow the PWR return to criticality. The transmutation rate and burnup calculation results indicate that 99Tc mixed homogeneously with BP may be a satisfactory 99Tc loading pattern in 99Tc transmutation in PWRs.